1. Field of the Invention
The present invention relates to a zoom lens, or a zoom lens barrel, which is provided with a cam mechanism for moving movable lens groups in the direction of the optical axis of the photographic optical system in a predetermined manner to obtain a continuously variable focal length upon zooming.
2. Description of the Related Art
A zoom lens having a cam mechanism for moving one or more movable lens groups which are guided in the direction of the optical axis of the photographic optical system (i.e., in the optical axis direction) without rotating about the optical axis in a predetermined manner by rotation of a cam barrel having cam grooves to obtain a continuously variable focal length is known in the art. In a typical cam mechanism of this type using cam grooves, the lens frame of each movable lens group is guided in the optical axis direction without rotating about the optical axis with the use of linear guide grooves which are formed on a linear guide barrel. This linear guide barrel is coupled to the cam barrel to be immovable in the optical axis direction relative to the cam barrel but rotatable about the optical axis relative to the cam barrel. When the lens frame of each movable lens group is inserted into the cam barrel so that the cam followers of the lens frame are respectively fitted in the corresponding cam grooves of the cam barrel, the lens frame is inserted into the cam barrel in a state wherein the end openings (the cam follower insertion openings) of the cam grooves of the cam barrel are positioned in alignment with the cam followers of the lens frame in the optical axis direction, respectively, while the linear guide grooves of the linear guide barrel are positioned in alignment with the linear guide projections formed on the lens frame in the optical axis direction, respectively. Therefore, in the case where two or more lens frames are supported by the cam barrel and the linear guide barrel therein, it is necessary to maintain accurate alignment between the cam barrel and the linear guide barrel in a circumferential direction every time before each lens frame is inserted into the cam barrel. This operation is troublesome and time-consuming.
The present invention has been devised in view of the above-mentioned problem, and accordingly, an object of the present invention is to provide a zoom lens having a cam mechanism which makes it easy to couple more than one lens frame to the cam barrel.
To achieve the object mentioned above, according to an aspect of the present invention, a zoom lens is provided, including a cam barrel driven to rotate about an optical axis; a first cam groove and second cam groove formed on an inner peripheral surface of the cam barrel, the first cam groove and second cam groove having different profiles;-a first lens frame having a first cam follower which is engaged with the first cam groove; and a second lens frame having a second cam follower which is engaged with the second cam groove. The first cam groove includes a first zoom section for moving the first lens frame between a telephoto position thereof and a wide-angle position thereof in accordance with a rotation of the cam barrel; a first leading section for leading the first cam follower from a first cam follower insertion opening, which is open at an end of the cam barrel, to the first zoom section; and a cam dead end positioned on the opposite side of the first zoom section with respect to the first leading section, wherein the first cam follower does not enter the cam dead end during operation of the zoom lens. The second cam groove includes a second zoom section for moving the second lens frame between a telephoto position thereof and a wide-angle position thereof in accordance with the rotation of the cam barrel; and a second leading section for leading the second cam follower from a second cam follower insertion opening, which is open at an end of the cam barrel, to the second zoom section. The cam dead end of the first cam groove and the second cam follower insertion opening of the second cam groove are formed at the same circumferential position in a circumferential direction of the cam barrel. Upon assembly of the first lens frame and the second lens frame to the cam barrel, the first cam follower is inserted into the first leading section via the first cam follower insertion opening, and subsequently, the second cam follower is inserted into the second leading section via the second cam follower insertion opening.
Preferably, the first cam follower, the second cam follower, the first cam groove, and the second cam groove respectively include a plurality of first cam followers, a plurality of second cam followers, a plurality of first cam grooves, and a plurality of second cam grooves, respectively provided at an equi-angular distance.
In an embodiment, the zoom lens further includes a linear guide barrel which is positioned inside the cam barrel so as to guide the first lens frame and second lens frame in the optical axis direction, the linear barrel including a linear guide slot extending parallel to the optical axis. The first lens frame includes a first guide projection and the second lens frame includes a second guide projection, the first guide projection and the second guide projection being engaged with the linear guide slot at different locations therein with respect to the direction of the optical axis. The first guide projection is formed on the first lens frame at the same circumferential position as the first cam followers. The second guide projections are formed on the second lens frame at the same circumferential position as the second cam followers. The first cam follower passes through the linear guide slot to be fitted in the first cam groove; and the second cam follower passes through the linear guide slot to be fitted in the second cam groove.
Preferably, the first lens frame includes a first resilient extending piece which extends in the direction of the optical axis to be elastically deformable in an inward radial direction; and the first guide projection is formed on the first resilient extending piece to extend radially outwards to be engaged with the linear guide slot; the first cam follower is fixed to the first guide projection to extend radially outwards to be engaged with the first cam groove via the linear guide slot; the second lens frame includes a second resilient extending piece which extends in the direction of the optical axis to be elastically deformable in an inward radial direction; the second guide projection is formed on the second resilient extending piece to extend radially outwards to be engaged with the linear guide slot; and the second cam follower is fixed to the second guide projection to extend radially outwards to be engaged with the second cam groove via the linear guide slot.
Preferably, the linear guide slot includes a plurality of linear guide slots, the first guide projection and second guide projection respectively include a plurality of first guide projections and a plurality of second guide projections, respectively equal to the number of the plurality of linear guide slots, and each of the first guide projections and corresponding one of the second guide projections are engaged with a common linear guide slot of the linear guide slots.
In an embodiment, the first cam groove further includes a first accommodation section positioned between the first zoom section and the first leading section. The second cam groove further includes a second accommodation section formed on the opposite side of the second zoom section with respect to the second leading section; and the first accommodation section and the second accommodation section are positioned in the same range in a circumferential direction of the cam barrel.
Preferably, the second cam groove further includes a stop section, wherein the depth of the stop section is smaller than the depth of the second zoom section in a radial direction of the cam barrel. The stop section is positioned in the middle of the second leading section to prevent the second cam follower from moving beyond the stop section, toward the cam follower insertion opening, when the second cam follower is fitted in the second cam groove.
Preferably, the linear guide barrel and the cam barrel are connected to each other to be relatively immovable in the direction of the optical axis and relatively rotatable about the optical axis.
According to another aspect of the present invention, a zoom lens is provided, including a cam barrel driven to rotate about an optical axis; a first cam groove and second cam groove formed on an inner peripheral surface of the cam barrel, the first cam groove and second cam groove having different profiles; a first lens frame having a first cam follower which is engaged with the first cam groove; a second lens frame having a second cam follower which is engaged with the second cam groove; and a linear guide barrel which is associated with the first lens frame and the second lens frame so as to guide the first lens frame and the second lens frame in a direction of the optical axis. The first cam groove includes a first zoom section for moving the first lens frame between a telephoto position thereof and a wide-angle position thereof in accordance with a rotation of the cam barrel; a first leading section for leading the first cam follower from a first cam follower insertion opening, which is open at an end of the cam barrel, to the first zoom section; and a cam dead end positioned on the opposite side of the first zoom section with respect to the first leading section, wherein the first cam follower does not enter the cam dead end during operation of the zoom lens. The second cam groove includes a second zoom section for moving the second lens frame between a telephoto position thereof and a wide-angle position thereof in accordance with the rotation of the cam barrel; and a second leading section for leading the second cam follower from a second cam follower insertion opening, which is open at an end of the cam barrel, to the second zoom section. The cam dead end of the first cam groove and the second cam follower insertion opening of the second cam groove are formed at the same circumferential position in a circumferential direction of the cam barrel. Upon assembly of the first lens frame and the second lens frame to the cam barrel and the linear guide barrel, the first cam follower is inserted into the first leading section via the first cam follower insertion opening, the linear guide barrel and the cam barrel are rotated relative to each other until the first cam follower reaches the cam dead end of the first cam groove, and subsequently, the second cam follower is inserted into the second leading section via the second cam follower insertion opening.
According to another aspect of the present invention, a zoom lens is provided, including a cam barrel driven to rotate about an optical axis; a first cam groove and a second cam groove formed on an inner peripheral surface of the cam barrel, the first cam groove and second cam groove having different profiles; a first lens frame having a first cam follower which is engaged with the first cam groove; a second lens frame having a second cam follower which is engaged with the second cam groove; and a linear guide barrel which is associated with the first lens frame and the second lens frame so as to guide the first lens frame and the second lens frame in a direction of the optical axis. The linear guide barrel is positioned inside the cam barrel and includes a linear guide slot extending parallel to the optical axis. The first lens frame includes a first guide projection which is engaged with the linear guide slot, and the second lens frame includes a second guide projection which is engaged with the linear guide slot. The first cam groove includes a first zoom section for moving the first lens frame between a telephoto position thereof and a wide-angle position thereof in accordance with a rotation of the cam barrel; a first leading section for leading the first cam follower from a first cam follower insertion opening, which is open at an end of the cam barrel, to the first zoom section; and a cam dead end positioned on the opposite side of the first zoom section with respect to the first leading section, wherein the first cam follower does not enter the cam dead end during operation of the zoom lens. The second cam groove includes a second zoom section for moving the second lens frame between a telephoto position thereof and a wide-angle position thereof in accordance with the rotation of the cam barrel; and a second leading section for leading the second cam follower from a second cam follower insertion opening, which is open at an end of the cam barrel, to the second zoom section. The second cam follower insertion opening and the linear guide slot are positioned to correspond to the second cam follower and the second guide projection, respectively, in a circumferential direction, when the first cam follower is positioned at the cam dead ends of the first cam grooves.
Preferably, the cam dead end and the second cam follower insertion opening are formed at the same circumferential position in a circumferential direction of the cam barrel.
Preferably, the linear guide slot is formed to penetrate through the linear guide barrel radially, wherein the first guide projection and the second guide projection are engaged with a linear guide slot at different locations therein in the direction of the optical axis; the first guide projection is formed on the first lens frame at the same circumferential position as the first cam follower; the second guide projection is formed on the second lens frame at the same circumferential position as the second cam follower; the first cam follower is fitted in the first cam groove via the linear guide slot; and the second cam follower is fitted in the second cam groove via the linear guide slot.
In an embodiment, the first lens frame includes a first resilient extending piece which extends in the direction of the optical axis to be elastically deformable radially inwards, wherein the first guide projection is formed on the first resilient extending piece to extend radially outwards to be engaged with the linear guide slot, and the first cam follower is fixed to the first guide projection to extend radially outwards to be engaged with the first cam groove via the linear guide slots. The second lens frame includes a second resilient extending piece which extends in the direction of the optical axis to be elastically deformable radially inwards, wherein the second guide projection is formed on the second resilient extending piece to extend radially outwards to be engaged with the linear guide slot, and the second cam follower is fixed to the second guide projection to extend radially outwards to be engaged with the second cam groove via the linear guide slot.
In an embodiment, the first cam groove further includes a first accommodation section positioned between the first zoom section and the first leading section, and the second cam groove further includes a second accommodation section formed on the opposite side of the second zoom section with respect to the second leading section. The first accommodation section and the second accommodation section are positioned in the same range in a circumferential direction of the cam barrel.
In an embodiment, the second cam groove further includes a stop section, the depth thereof being smaller than the depth of the second zoom section in a radial direction of the cam barrel. The stop section is positioned in the middle of the second leading section to prevent the second cam follower from moving toward the cam follower insertion opening beyond the stop section when the second cam follower is fitted in the second cam groove.
Preferably, each of the first cam follower, second cam follower, first cam groove, and second cam groove includes a plurality of first cam followers, second cam followers, first cam grooves, and second cam grooves, respectively provided at an equi-angular distance.
Preferably, the linear guide slot includes a plurality of linear guide slots, the first guide projection and second guide projection respectively include a plurality of first guide projections and a plurality of second guide projections, respectively equal to the number of the plurality of linear guide slots, and each of the first guide projections and corresponding one of the second guide projections are engaged with a common linear guide slot of the linear guide slots.
According to another aspect of the present invention, a zoom lens is provided, including a cam barrel driven to rotate about an optical axis; a first cam groove and second cam groove formed on an inner peripheral surface of the cam barrel, the first cam groove and second cam groove having different profiles each other; a first lens frame having first a cam follower which is engaged with the first cam groove; a second lens frame having a second cam follower which is engaged with the second cam groove; and a linear guide barrel which is associated with the first lens frame and the second lens frame so as to guide the first lens frame and the second lens frame in a direction of the optical axis. The first cam groove includes a first zoom section for moving the first lens frame between a telephoto position thereof and a wide-angle position thereof in accordance with a rotation of the cam barrel; and a first leading section for leading the first cam follower from a first cam follower insertion opening, which is open at an end of the cam barrel, to the first zoom section. The second cam groove includes a second zoom section for moving the second lens frame between a telephoto position thereof and a wide-angle position thereof in accordance with the rotation of the cam barrel; and a second leading section for leading the second cam follower from a second cam follower insertion opening, which is open at an end of the cam barrel, to the second zoom section. The first cam groove is formed so that the first cam follower insertion opening and the first zoom section are formed on opposite sides of the second zoom section in the direction of the optical axis, and the first leading section is formed on the first cam barrel to detour around an adjacent the second cam groove so as not to overlap the adjacent second cam groove.
Preferably, the first cam follower, the second cam follower, the first cam groove, and the second cam groove respectively include a plurality of first cam followers, a plurality of second cam followers, a plurality of first cam grooves, and a plurality of second cam grooves, respectively provided at an equi-angular distance.
In an embodiment, the first cam groove further includes a cam dead end positioned on the opposite side of the first zoom section with respect to the first leading section, the first cam follower not reaching the cam dead end during operation of the zoom lens. The cam dead end of the first cam groove and the second cam follower insertion opening of the second cam groove are formed at the same circumferential position in a circumferential direction of the cam barrel. Upon assembly of the first lens frame and the second lens frame to the cam barrel and the linear guide barrel, the first cam follower is inserted into the first leading section via the first cam follower insertion opening, the linear guide barrel and the cam barrel are rotated relative to each other until the first cam follower reaches the cam dead end of corresponding one of the first cam grooves, and subsequently, the second cam follower is inserted into the second leading section via the second cam follower insertion opening.
Preferably, the linear guide barrel is positioned inside the cam barrel, the linear barrel including a linear guide slot extending parallel to the optical axis, wherein the first lens frame includes a first guide projection and the second lens frame includes a second guide projection, the first guide projection and the second guide projection being engaged with a linear guide slot at different locations therein in the direction of the optical axis. The first guide projection is formed on the first lens frame at the same circumferential position as the first cam follower; and the second guide projection is formed on the second lens frame at the same circumferential position as the second cam follower. The first cam follower is fitted in the first cam groove via the linear guide slot; and the second cam follower is fitted in the second cam groove via the linear guide slot.
In an embodiment, the first lens frame includes a first resilient extending piece which extends in the direction of the optical axis to be elastically deformable radially inwards; the first guide projection is formed on the first resilient extending piece to extend radially outwards to be engaged with the linear guide slot; and the first cam follower is fixed to the first guide projection to extend radially outwards to be engaged with the first cam groove via the linear guide slot. The second lens frame includes a second resilient extending piece which extends in the direction of the optical axis to be elastically deformable radially inwards; the second guide projection is formed on the second resilient extending piece to extend radially outwards to be engaged with the linear guide slot; and the second cam follower is fixed to the second guide projection to extend radially outwards to be engaged with the second cam groove via the linear guide slot.
Preferably, the linear guide slot includes a plurality of linear guide slots, the first guide projection and second guide projection respectively include a plurality of first guide projections and a plurality of second guide projections, respectively equal to the number of the plurality of linear guide slots, and each of the first guide projections and corresponding one of the second guide projections are engaged with a common linear guide slot of the linear guide slots.
In an embodiment, the first cam groove further includes a first accommodation section positioned between the first zoom section and the first leading section; and the second cam groove further includes a second accommodation section on the opposite side of the second zoom section with respect to the second leading section. The first accommodation section and the second accommodation section are positioned in the same range in a circumferential direction of the cam barrel.
Each above-described aspect of the zoom lens of the present invention can, for example, be incorporated in a digital camera.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2000-23512 (filed on Feb. 1, 2000) which is expressly incorporated herein by reference in its entirety.